When does your cervix open during pregnancy?

id really depends. when the cervix opens, it is called dialating. for example, i was due April 19th. however, march 29th i was dialated to 3 cm. in my case, i had my baby that day because he was "frank breech" so they are to do a c-section. but some girls go weeks being 1-3 cm dialated, it just depends, and usually happens the closer you approach your due date :) hope this was helpful!